System Administrator

The System Administrator (SA) is primarily responsible for the smooth operation of the System.It is a SA s job to switch on the system console.(The machine on which the Operating System resides , also known as the server machine.) The SA also creates users and groups of users for the system and tasks backup to prevent loss of data due to system break down.In Linux the SA is also known as the root user. The SA has all the right for the Linux System.

File Owner

The User who creates a file is said to be the owner of that file.The owner of a file can perform any operation on that file coping , deleting ,editing.

Group Owner

Consider the following Situation.
a project team of 5 people from the Esoft Metro Campus is working on a software development project for a private detective agency. An analyst heads the team. The other four members are programmers.The team is working on a Linux System.Each programmers has been given a few programs to develop.the data provided by the detective agency is of a highly confidential nature.and so the data file has been created in the analyst's HOME directory. one programmer may have to link(join) a program to another programmers programming in order to test the program.
In this situation each programmer is the file owner of his or her own program files.Each program,how ever also belongs to  the other programmers.so that they can use it for linking to the file or directly access the file. The Project team of five users is said to be the Group owner for the file . In Linux It is possible to define the users who will belongs to a group. a group of users are also given a name ,  just as a user is given a name.

Other Users

 In the example of the Esoft Metro Campus , all the users of the System who are not members of the project groups are referral to as other users for the  files of that group.Their Users are users who do not belongs to the particular group. For Example, the Users belongs to the finance department could be treated as other users for the payroll department.

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The ring topology connects the nodes on a network through a point to poinr connection. Consequently, no end points exist in this type of setup.
The following figure shows a typical ring-based setup.

In the preceding figure all computers are connected in  a ring-like layout.As a result,similar to the bus topology, the main cable is the only transmission path.How ever, unlike the bus topology, data packet can ravers only in a unidirectional format.
When a node receives a data packet ,it reads the data packet and regenerates it to restore its original strength. The packet is then passed to the neighboring node. The data packet navigates the network in this format until the destination nodes receives the packet.

Advantages

Prevention of Collisions

The ring topology prevents network collisions by using the token ring access method. According to this method, if a node needs to transmit data, it must acquire a token that circulate through the ring. when the node acquire the token ,the node uses the token to transfer its data to the destination node. Until the current node releases the token other node cannot transmit data and must wait for their turn to acquire the token. As a result, the possibility of any collision in this step is 0.

Ease in troubleshooting and maintenance

Its easy to locate cable faults in ring setup.In cable related fault, the nodes that is next to failed cable segment can indicate the fault when it fails to receive a signal within the specified time limit.

Limitations

High Risk of network Failure

On a ring network, the nodes are connected through a point to point connection. If one of node on the network malfunctions , the entire network stops functioning.

Expensive Setup and Installation

The Device and Cabling  required to setup a ring network are more expensive than any other topology.

The star topology connects nodes over a network using a central control unit called the Concentrater(Hub), Concentrater can be a Hub, a switch or a router. The hub is a device that transmits information from one node to another.
The following figure shows a typical star topology setup

In preceding figure , All computers are connected through a hub. If a computer transmit data to an another computer , Each data packet from source computer is firstly sent to the hub.The hub ,in turn, sends data packets to destination computer.

Advantages

Higher Scalability
 Can easily add nodes to a star based network by attaching the required node to the hub. How ever the number of nodes that you can connect to the hub depends on the capacity of the hub.

Ease in troubleshooting and maintenance.
It is easy to locate fault in a star setup.If a node becomes faulty, It does not affect the working of the hub, which,in turn,does no affect the other nodes of the network

Limitations

High Cost of Installation

Setting up a star topology requires a lot of cabling because all the nodes have to connect to the hub. in addition the hubs are very expensive.

Single Point of Failure

The hub is a single point for handling network communication. As a result , a failure in the hub can disrupt the entire network communication.

The bus topology connects all the nodes on a network to a main cable called bus, as shown in the following figure

In the preceding figure Computers are connected through the bus, When a Computer needs to transmit data to an another computer , Is sends the data over the bus in the form of data packets. In the bus topology each packet placed on the bus contains the address of the destination node. The packet is transmitted in both directions along the bus. In other words,The data packet is sent to all the nodes in the network.Each node on the network, which receive a data packet compares the destination address of the packet with its own address. If the two address match the nodes, reads the data packet else it ignore the packet.

A device call Terminator is attached to each end of the bus As the name suggest , the terminator receives signal that have traversed through the bus and  terminates them.The termination of signals ensures that signals that have already traversed through the bus do not collide with new signals.

In the Bus topology data packets may collide if multiple nodes transmit signal at the same time. to prevent this situation, the bus topology provides a collision detection mechanism called Carrier Sense Multiple Access with Collition Ditection (CSMA/CD) . This Mechanism resolves the collisions that may occur if multiple nodes transmit data packet simultaneously.

Advantages

• Easy Installation
• Require Minimum cabling
• Relatively inexpensive
• Cost of cabling is less

Limitations

Low fault tolerance

• The Bus topology is highly prone to faults. If the bus connecting the computers malfunctions, the entire network communication is disrupted. As a result, the bus is single point of failure (SPOF) on the network

Inability to handle high network traffic

• In the bus topology, only one nod can transmit packets at any instance. If multiple nodes transmit data packets simultaneously, it leads to network collisions. As a result the higher the number of nodes on the bus, the lower is its performance. According to specifications,only 15 nodes can be connected to a bus of 30 meters.
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Lower Scalability

• Adding nodes to an existing bus topology network is difficult.To add a node to the net work, the entire network cable setup needs to be reconfigured.I addition , the length of the cable used for the topology has a physical limitation of 30 meters.It cannot expanded beyond this limit. As as a result ,the number of nodes that can be attached to the network is limited.
• 
  

Difficulty in Troubleshooting and maintenance

• If a problem occurs on a node in the bus topology , troubleshooting become time-consuming. This is because the administrator needs to check every point on the step to locate the fault.

Network topology is a schematic layout or map of the arrangement of nodes over a network.This layout also determines the manner in which information is exchange within the network

The different types of topologies that can be used to set up a network are

• Bus
• Star
• Ring
• Mesh

Moved To
http://www.lankageek.com/what-are-the-network-topologies/

This is the 2nd Part of this title. 1st Part you can catch from here
http://lionsit.blogspot.com/2014/10/types-of-files-in-linux.html

Special Files

Most of the System file in Linux are special files are typically associated with input/output device and are found in the standard Linux directories, such as  /dev and /etc . User Cannot Alter special files.

Linux supports the following types of special files:

• Character Device files
• Block Device Files
• Hard Links
• Symbolic Links

Character Device Files

Read and write data one character at a time. A modem is an example of a character device file.Character device are also called Sequentially access device.

Block Device File

Can Access a block of data at a time, Generally a block of data can be either 512 or 1024 bytes. Here, the kernel reads or write minimum one block of data at a time.The Kernel collects the data in the memory for the amount of block memory and then makes iti available to user. Such Devices Allow Random Access. This makes input output operations faster 

Eg :Hard Disk

Many of Devices can act as character device or block device depending on the command that is used access the devices.

Hard Links

Special files that allow a single file to have multiple names You can have a hard link file only for a file not a directory.directory. These links are known as hard links because they create a direct link to an inode. Since each file System has its own inode information database,you can hard link files only when there on the same file System;

Symbolic Links

Also known as Soft Links, are similar to hard links except they can work across different file Systems

In Linux all information is treated as a file. So , Besides user's program files and data files, there are also special files such as those that contain information about directory contents of the various input/output devices connected to the system, In Linux Device is also treated as a file and all the information going to say the VDU(Visual Display Unit) is treated as if it ware being sent to a file. In Linux  There are  3 categories of files.

• Ordinary Files
• Directory Files
• Special Files

Ordinary Files

All the Files created by an user come under this category of files. These include 

All the data files

Program files

Object Files

Executable Files

A user can Make changes to this kind of files.

Directory Files

Linux automatically creates a directory file when a directory is created. This file has the same name as the Directory, and  contains information about the files under the directory.For Example , for the directory   /home/asela, There will be a directory file called asela in the directory,/home which contains information on all the files and directories under the directory, asela . A Directory file cannot be modified by a user but is, instead ,modified automatically by the System when a new file or a sub-directory is added to the directory.

Special Files 

I will Explain it in Next Post


http://lionsit.blogspot.com/2014/10/types-of-files-in-linux-2.html

There is a Pretty good and Millions lol Message I heard today about Tsu.co New developing social networking site which pay to their members. they tell they pay 90% present from their profit and they already have US $ 7 Million fund. lot of people trying hard to collect some money but there is several problems there. http://www.girlfriendsocial.com has Explained these problems simply. as their mentioning problems.

1. Advertising Model
Before withdraw you have to $100 in your Account. If you try hard in whole day You will can earn $1 per a day. So You Can Earn $100 in 3 Months. And Your Electricity Bill and Internet Bill Will be Enthusiastic. As an Example
Facebook Income 2013 -  $ 7.87 Billion    =>  10 B
Facebook Users   1.32 Billion =>                     1 B

Facebook Can give you all to 10B* 90% =    US $ 9 Billion

Your Income for an Year                        =  9B/1B   =  US $ 9 // LOL

So How TSU.co will pay you that amount. 

2)It is a Illegal

They are using MLM Pyramid System. Go to below link and Check Updates. Even You never invest money think about your time investment with pressure.
http://www.vandruff.com/mlm.html


3) Their Profit Insufficient 

They takes only 10%  from their Income. How TSU.co Upgrade Servers Systems and pay for employee and manage their other expensive.

4) Technical Problems

They are Still Using fever Technology. still they not using Https. When you sent a request TSU will be display it to friend in next hour. :D

If you want to try go ahead and try and Never give them to your Transaction Details .
Tsu.co

After Install Ubuntu Lot of Users may have a doubt What  I should do next. You can use tweak tools to change your desktop appearance to pretty good. Then You have to find some Applications to install. Can use Terminal or Package Installer to achieve that but necessary to one by one type or Install. 

But now you can use “Ubuntu After Install”  to perform this task easily. If you are using later version of Ubuntu 12.04 (12.04, 12.10,13.04,13.10,14.04,14.10) You can Install “Ubuntu After Install” and It Comes with lot of software collection and you can Install those in single click.

Installing

1) Get The Terminal

Ctrl + Alt +T 

2) Type Following Commands 

sudo add-apt-repository ppa:thefanclub/ubuntu-after-install

sudo apt-get update

sudo apt-get install ubuntu-after-install

3) After Install You Can Find “Ubuntu After Install” under Application

4) Then Select Applications and Press Install Now 

Application List Comes With “Ubuntu After Install”

• Ubuntu Restricted Extras: video codecs , Flash Plugin
• libdvdcss DVD playback
• Unity Tweak Tool  desktop settings tweaking 
• Variety wallpaper changer for Ubuntu
• Google Chrome  The Web Browser
• LibreOffice Office Software Collection
• Skype Video Calling 
• Grive Tools Sync With Google Drive
• DropBox Sync With Drop Box
• VLC Media Player
• XBMC Home Media Center
• Radio Tray Streamer Online radio
• GIMP Like Photoshop
• Darktable  RAW files
• Inkscape vector based illustration
• Scribus desktop publishing 
• Samba network sharing server allows Windows
• PDF Tools edit PDF documents
• OpenShot  Popular video editor 
• Kdenlive advanced video editor
• Handbrake Multimedia Converter
• Audacity Sound Editor
• Steam The gaming platform
• KeePass Password Manager
• Shutter screenshots
• FileZilla FTP 
• p7zip compression and decompression tool
  
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A new Threat founded by American Specialist effected to world wide Android users. As the reports they warned to android users to be careful when install Flashlight Free Apps . Those Applications are  trying to track and steal users data as well as your personal SMS too.
After stealing Those information Its deliver to Spammers and Hackers. So When you are installing below and other Flashlight Application You have to consider twice about your Security .

• Super Bright LED Flashlight, 
• Brightest Flashlight Free 
• Tiny Flashlight+ LED